Hello, I have an ARP soloist (non-PRO soloist, the original) that I've been using for a while (and am in love with). Recently the keyboard has gone out of tune with itself - the top octave (B2-C3) is out of tune with the rest of the keys down.

I had a knowledgeable friend help me diagnose and we've diagnosed it down to IT LIKELY being a problem with the original 4027 circuit. It could likely be fixed - IF - the 4027 wasn't an epoxy filled/sealed unit. We were hoping it was just a needed adjustment to the trimmers inside...but alas, the trimmer responsible for the upper octave IS functioning as it should...yet no adjustments are working (problem is therefore likely on the 4027 side). The trimmer for the rest of the octave down DOES adjust as it should however.

However, I do want to double-check and found your site...hoping for help. I wanted to run this by you all and see what ARE ALL THE POSSIBLE CULPRITS (along with the 4027)...just so I make sure to check all the bases.

I'm a performer and not a pro tech. I repair my own Hammond B3 (mostly mechanicals, etc.) while my incredible friend helps me with all the amp (tube/solid state) issues.

Can you tell me about the ARP soloist, about tuning and problems like this...possible things to check, likely culprits?

About the 4027 onboard this ARP, can it be "UN-EPOXYED" (so we might get to the problem parts for repair)?

Anyone know the schematic and full parts info for the original 4027 in this ARP Soloist (also the same as the 4027 in the ARP 2600?)...that is IF we can get epoxy out and get into it?

Thank you for any help on the matter. It was working great up until lately
Really love it and want to fix as it's become part of me and what I do live (Hammond organ, ARP).

I want to be sure though that the 4027 is actually the issue (out of tune with itself, mainly the last top octave from the rest of the keyboard (B2-C3). The trimmer (tested working) "should" be tuning that top octave...but it does nothing. And the only trace goes to the pin on the 4027...therefore we have to assume the problem lies within the 4027 module somewhere.
I of course am repeating the info he gave me

The 4027 module is still attached to the board, I have not taken it off (yet), so I am NOT SURE it's "epoxy-filled". I'm going by what my tech friend guesstimated (likely correct there)

But I say this because I received a reply via email on my search for help with this ARP. He says:

Fwiw, most epoxie Arp modules are not filled with epoxy.
They're either hollow (air) or soft white silicone rubber as used in bathroom caulks.
It is possible to crack the outer shell and pick out all the rubber inside.
I've fixed plenty of arp sub-modules this way.

"Fwiw, most epoxie Arp modules are not filled with epoxy.
They're either hollow (air) or soft white silicone rubber as used in bathroom caulks.
It is possible to crack the outer shell and pick out all the rubber inside.
I've fixed plenty of arp sub-modules this way.

I'd try verifying for sure it's the sub-module.
If possible, repair it yourself.
Or buy one of the knock offs available on Ebay or through CMS.
You can short the in to out on a removed submodule like the filter and tho there'd be no filtering, the audio signal path would remain intact and easier to troubleshoot other problems."

I'd sure love to fix this thing.

Can anyone tell me about the knock-offs (4027)? What is the trade off there?...sound/tone?

I want to be sure though that the 4027 is actually the issue (out of tune with itself, mainly the last top octave from the rest of the keyboard (B2-C3). The trimmer (tested working) "should" be tuning that top octave...but it does nothing. And the only trace goes to the pin on the 4027...therefore we have to assume the problem lies within the 4027 module somewhere.
I of course am repeating the info he gave me

The 4027 module is still attached to the board, I have not taken it off (yet), so I am NOT SURE it's "epoxy-filled". I'm going by what my tech friend guesstimated (likely correct there)

I'd sure love to fix this thing.

Can anyone tell me about the knock-offs (4027)? What is the trade off there?...sound/tone?

As you can see, an answer was a couple years in coming, but more than welcome when it came.

As for the Soloist modules I have, I tried cutting into the shell of one of the fixed filter modules, and it is indeed completely filled with epoxy. They are heavy. I would imagine yours are probably filled solid also.

That said, check your module to see if it is a 4027, or a 4027-1. Both types were used in the 2600, not sure about the Soloist. The modules are NOT the same. I've attached the relevant page from the 2600 Service Manual below. Either way, there is nothing inside either module that is adjustable. Yes, it is possible something inside is dying, but there are other things to check first. This assumes the power supply voltages have been checked and are correct:

1. Attach a Voltmeter lead to Pin 2 of the VCO. It doesn't matter which flavor module you have, Pin 2 is the CV input on both.

2. Play the lowest C. If it is tuned the same as the 2600, there should be sound, but 0V on Pin 2. If not, don't panic yet, and don't adjust anything yet either. Just make a note of the Voltage (no pun intended) when playing Low C.

3. Play the highest C. It should be exactly 3V if Low C is 0V, or exactly 3V higher than the low C Voltage. (Don't go by the 4V mentioned in the 2600 manual, its keyboard has an additional octave).

Here's what to try IF the Voltages are not correct:

1. Clean the keyboard buss bar(s), and the J-wires to each key (I probably don't need to tell you to be careful!)

3. If your VCO is indeed a 4027-1, the High Frequency Tracking trimmer is not connected, and shouldn't be affecting anything at all when turned. If it is an original 4027, check to see if in fact the resistance between Pin 11 and Pin 15 changes as the trimmer is turned. Check this AT Pin 11 and Pin 15, not at the pins of the trimmer. If the resistance doesn't change between pins 11 and 15, check for bad solder joints or broken traces between the trimmer and the module (This includes Pin 14 also). Check to make sure the resistance between Pin 14 and Pin 15 is 10K, or very close to 10K. If not, check it at the trimmer itself. If the trimmer is not 10K, replace the trimmer.

If none of the above works, let us know, I'll try to think of something else.

P.S. - Oh yeah, if there are any tantalum bead capacitors remaining in the thing, REPLACE them with new electrolytic caps of appropriate value and Voltage. In EVERY ARP I've ever worked on, those old tantalum caps were the cause of some, if not all, of the problems.

P.P.S. - I've attached a photo of my 4027 module. It is a 4027, NOT a 4027-1. It actually weighs a little more than the filter modules do, so I'm positive that it is indeed epoxy-filled. Also, unlike the service manual for the 2600 states, my 4027 only has 10 pins.

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